Indicator lamp in a transistor emitter follower circuit with a lamp warmup resistor in parallel with the transistor



June 3 R. J. PETSCHAUER 3,333,293

INDICATOR LAMP IN A TRANSISTOR EMITTER FOLLOWER CIRCUIT WITH A LAMP WARMUP RESISTOR IN PARALLEL WITH THE TRANSISTOR Filed May 20, 1965 III INVENTOR. 21mm JPnsamm Mfiw' ATTOE/VEVS' United States Patent INDICATOR LAMP IN A TRANSISTOR EMIT- TER FOLLOWER CIRCUIT WITH A LAMP WARMUP RESISTOR IN PARALLEL WITH THE TRANSISTOR Richard J. Petschauer, Minneapolis, Minn., assignor to Fabri-Tek Incorporated, Minneapolis, Minn., a corporation of Wisconsin Filed May 20, 1965, Ser. No. 457,356 5 Claims. (Cl. 315-175) ABSTRACT OF THE DISCLOSURE as removing the need for input impedance networks to the switching transistor.

This invention is concerned with control apparatus and more particularly with a transistorized indicator lamp circuit.

Indicator lamps find vast use in contemporary industry. By way of example, indicator lamps are often used in such items as computer consoles, machinery panels, and traffic panels. The need for and use of indicator lamps stretches from childrens games to hospital operating rooms. Often the number of indicator lamps used in a single device becomes extremely large, such as in a computer console where a vast number of lamps may be used to indicate the true or false state of the computer bistable stages.

One problem which arises when a large number. of indicator lamps must be used is the large load placed on the source of control signal energy by the circuits which control the indicator lamps. Another problem is the cost of the components which go to make up the control circuit for the indicator lamps.

The apparatus of this invention provides an indicator lamp circuit which presents a decreased load to the source of signal energy. Further, the apparatus of this invention provides an indicator lamp circuit made up of fewer components than presently known circuits.

Briefly described, this invention uses a grounded-collector transistor to drive a lamp connected in circuit with the transistor emitter electrode. A resistor is serially connected with the lamp across the source of electrical energy, and is of such a magnitude to prevent the lamp from coming on when the transistor is off, but to allow a sufiicient amount of current to pass through the lamp to keep it in a standby or preheated stage for fast turnon. Since a grounded-collector transistor configuration is used, the circuit gain is greater than that of the presently used grounded-emitter transistor configurations. Therefore, a reduced load is presented to the source of signal energy which turns the transistor off and on. Also there is no need for an input impedance network to the transistor base electrode, which again reduces the load to the signal energy, and lowers the number of components needed to drive the lamp.

In the drawings,

FIG. 1 is a schematic representation of a first embodiment of the circuit of this invention utilizing a NPN transistor; and

FIG. 2 is a schematic representation of a second em- 3,388,293 Patented June 11, 1968 bodiment of the circuit of this invention using a PNP transistor.

Referring now to FIG. 1, there is shown a source of energy, here shown as a battery 10, having its positive terminal connected to a common ground. There is also shown an NPN transistor 15 having an emitter electrode 16, a collector electrode 17, and a base electrode 18. C01- lector electrode 17 is connected to the common ground. Emitter electrode 16 is connected through a lamp 13 to the negative terminal of battery 10. A resistor 14 is connected intermediate emitter electrode 16 and collector electrode 17. Base electrode 18 is connected to an input terminal 20, and collector electrode 17 is connected to an input terminal 21.

Referring now to FIG. 2, there is again shown a source of energy as a battery 10, now having a negative terminal connected to a common ground. There is also shown a PNP transistor 25 having an emitter electrode 26', a collector electrode 27, and a base electrode 28. Collector electrode 27 is connected to the common ground. Emitter electrode 26 is connected through lamp 13 to a positive terminal on battery 10. A resistor 14 is connected intermediate emitter electrode 26 and collector electrode 27. Base electrode 28 is connected to an input terminal 20, and collector electrode 17 is connected to a input terminal 21.

In discussing the operation of the circuit of FIG. 1, first assume that a negative control signal is present at input 20. This negative .bias on base electrode 18 will back bias the emitter-base junction of transistors 15 to hold transistor 15 off. Therefore, substantially the only current flowing in the circuit will be from the positive terminal of battery 19, through the common ground, through resistor 14 and lamp 13 to the negative terminal of battery 10. The magnitude of the resistance of resistor 14 is chosen such that this current is not suflicient to light lamp 13 (that is, lamp 13 is not sufficiently incandescent to be visible to the human eye) but is enough to cause a preheating of lamp 13.

Now assume that the control signal to input terminal 20 becomes positive. This b-ias will be felt on base electrode 18 and cause a forward biasing of the base-emitter junction of transistor 15, to cause a current to flow from base 18 to emitter 16, to turn on transistor 15. A current will then flow from the positive terminal of battery 10, through the common ground, from collector 17 to emitter 16 of transistor 15, and through lamp 13 to the positive terminal of battery 10. This current will be sufiicient to light lamp 13. Since lamp 13 has been preheated by the above described current flow through resistor 14, the initial surge current through transistor 15 during its turnon will be much less than the surge current necessary to light lamp 13 had lamp 13 been cold. This lower surge current will have the effect of a lower load felt by the source of control energy (not shown). Also inasmuch as transistor 15 is connected in a grounded-collector configuration, the load felt by the source of control energy will be less than had transistor 15 been connected in the usual grounded-emitter configuration. This latter feature is possible because the gain of a grounded-collector transistor amplifier is substantially equal to the gain of the transistor, while the gain of a grounded-emitter transistor amplifier is equal to approximately /3 to /2 the gain of the transistor. This discrepancy is due to the fact that grounded-emitter transistor stages normally require some impedance network at the control input to insure proper or satisfactory operation. This input impedance network will attenuate the input signal, thus causing an increase in the load to the source of control energy.

The operation of the circuit of FIG. 2 is essentially similar to that of the circuit of FIG. 1, with the exception that the transistor 25 is a PNP transistor as opposed to the NPN transistor 15 of FIG. 1. Assume in FIG. 2 that the control input to input terminal 20 is positive. This positive bias will be felt on base 28 to back bias the emitter-base junction of transistor 25 to keep transistor 25 off. A current will then flow from the positive terminal of battery 10, through lamp 13 and resistor 14, and through the common ground to the negative terminal of battery 10. As was the case in the operation of the circuit of FIG. 1, the magnitude of resistance of resistor 14 is chosen such that this last described current is sufiicient to preheat lamp 13, but not suflicient to cause visible incandescence. Assume now that the control signal to input terminal 20 becomes negative. This negative bias will be felt on base electrode 28 to forward bias the emitter-base junction of transistor 25 causing a current flow from either emitter electrode 26 -to base electrode 28. This will cause transistor 25 to turn on and a current will flow from the positive terminal of battery through lamp 13, from emitter electrode 26 to collector electrode 27, and through the common ground to the negative terminal of battery 10. As was the case in the circuit of FIG. 1 the turn-on or surge current of transistor 25 will be less, due to the fact that lamp 13 had been preheated. Also, the grounded-collector configuration of transistor 25 will have the same effect of lowering the load to the source of control energy (not shown).

It is thus apparent that this invention as described above comprises a unique transistorized lamp circuit capable of lighting a given lamp with fewer components, and at the same time presenting a lower load impedance to the source of control energy. Especially when applied to situations in which a large number of indicator lamps are necessary, such as computer consoles, this savings in components and control power represents an important advance over the prior art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A semiconductor lamp circuit comprising:

a source of energy;

multi-junction semiconductor switch means including input, output and control electrodes;

means connecting said output electrode to a first terminal on said source of energy; lamp means; means connecting said lamp means intermediate said input electrode and a second terminal on said source of energy;

impedance means connected intermediate said input and output electrodes; and

a pair of input terminals connected, respectively, to

said control electrode and said output electrode and adapted to receive control signals for turning said semiconductor switch means otf and on.

2. Indicator lamp circuit apparatus comprising:

a source of energy;

a multi-junction transistor having emitter, collector and base electrodes;

means connecting said collector electrode to one terminal on said source of energy;

an indicator lamp;

means connecting said indicator lamp intermediate said emitter electrode and another terminal on said source of energy;

impedance means connected intermediate said collector and emitter electrodes; and

a pair of input terminals connected, respectively, to

said base electrode and said collector electrode and adapted to receive control signals for varying the conductive state of said transistor.

3. A transistorized lamp circuit comprising:

a source of electrical energy having positive and negative terminals;

a NPN transistor having emitter, collector and base electrodes;

means connecting said collector electrode to said positive terminal;

a lamp;

means connecting said lamp intermediate said emitter electrode and said negative terminal;

a resistor connected intermediate said collector and emitter electrodes; and

a pair of input terminals connected, respectively to said base electrode and said collector electrode and adapted to receive control signals for changing the conductive state of said NPN transistor.

4. A transistorized lamp circuit comprising:

a source of electrical energy having positive and negative terminals;

a PNP transistor having emitter, collector and base electrodes;

means connecting said collector electrode to said negative terminal;

a lamp;

means connecting said lamp intermediate said emitter electrode and said positive terminal;

a resistor connected intermediate said collector and emitter electrodes; and

a pair of input terminals connected, respectively, to said base electrode and said collector electrode and adapted to receive control signals for changing the conductive state of said PNP transistor.

5. A transistorized indicator lamp circuit comprising:

a source of electrical energy;

a multi-junction transistor having emitter, collector and base electrodes;

means connecting said transistor in grounded-collector configuration across said source of electrical energy, said means including an indicator lamp;

control means connected to said base electrode and said collector electrode for turning said transistor off and on; and

impedance means connected in parallel with said transistor and in series with said indicator lamp, so that when said transistor is off a preheat current flows through said indicator lamp.

References Cited UNITED STATES PATENTS 2,407,113 9/1946 Tuck 315-36 2 X 2,780,752 2/ 1957 Aldrich et al. 315-240 2,972,706 2/1961 Malrn et al. 315-225 3,022,467 2/1962 Leeder 331-74 3,046,494 7/ 1962 Root 315136 X 3,157,870 11/1964 Marino et al. 315-132 X 3,263,119 7/1966 School 315-77 3,212,020 10/1965 Donovan et a1 330--24 X 3,259,841 7/1966 Proctor et a1. 33014 X FOREIGN PATENTS 1,010,201 11/1965 Great Britain. 1,014,104 12/ 1965 Great Britain.

JAMES W. LAWRENCE, Primary Examiner. C. R. CAMPBELL, Assistant Examiner. 

